Gemini Dark Matter

TL;DR

The Gemini dark matter model proposes a nearly degenerate twin-particle system with decay properties that can resolve the $S_8/\sigma_8$ tension in large scale structure, predicting observable dark radiation signatures.

Contribution

It introduces a novel dark matter model with twin particles and a decay mechanism linked to Froggatt-Nielsen symmetry, addressing the $S_8/\sigma_8$ tension.

Findings

Decaying twin dark matter can resolve the $S_8/\sigma_8$ tension.

Dark matter mass is in the keV range, acting as cold dark matter.

Model predicts detectable dark radiation in future CMB measurements.

Abstract

The $S_8/\sigma_8$ tension in the large scale structure can be explained by decaying dark matter with an almost degenerate spectrum and small enough decay width. Here we propose the Gemini dark matter model, which contains a heavy mother particle $\chi_3$ and two twins $\chi_{1/2}$ which are almost degenerate in mass and are produced at the same time. The dark sector is charged under the same Froggatt-Nielsen symmetry that can explain the hierarchy of the Standard model Yukawa couplings. The slightly heavier $\chi_2$ decays into $\chi_1$ and the axionic component of the flavon, which washes out the small scale structure and resolves $S_8/\sigma_8$ tension. We present the production mechanism of Gemini dark matter and viable parameter regions. We find that despite the preferred dark matter mass being $\mathcal{O}(1)$--$\mathcal{O}(100)$ keV, they constitute cold dark matter. The Gemini dark matter model predicts an abundance of dark radiation that will be probed in future measurements of the cosmic microwave background.